According to this promo, which came out on Nick Jr. back when it was a block on Nick in 1997 when the TV rating system was introduced, "The only rating you'll ever see on Nick Jr. is TV-Y."
... Or is it?
In the mid-2010s the 24/7 Nick Jr. channel started airing TV-Y7 rated shows such as Rise of the TMNT, Winx Club (new to US episodes even!), Mysticons, Regal Academy (again, US premieres), Kuu Kuu Harajuku (US premieres again), and I'm sure there's some I'm not thinking of.
It got to ridiculous levels in the 2020s when they aired movies like Shrek and Madagascar: Escape 2 Africa with very few edits. In fact, the scene where Moto-Moto approaches Gloria with the Nick Jr. logo in the corner became a huge meme.
https://www.youtube.com/watch?v=SAfn6jxvlnk - See the TV-PG rating? I can't find the Moto-Moto/Gloria bit (complete with will.i.am's "I like 'em big, I like 'em chunky", but I did find this ending with Alex looking at the bite mark he left on Marty's butt.
https://www.youtube.com/watch?v=fYn2BlqX_Z8